Can I stay in the TSP past age 70 1/2

I don’t want to spend my Roth TSP balance at age 70 1/2 and I want to stay with TSP. What do I do?

How can I MAX the amount of my rollover of my Roth TSP to a Roth IRA given proportional rule and want to stay in TSP? My Traditional TSP balance is 200K and Roth TSP balance is 50K… Do I do partial withdrawal of 200K which would allow me to rollover 50K to Roth IRA and rollover 150K back to TSP?

You’re on the right track. You can do a rollover (which would have to be proportional) from the TSP and then roll the traditional balance back into the TSP. You need to have at least $200 in your TSP account to keep it open, so be sure to leave at least that amount in the TSP when you do your rollover.
Here’s an example: You can roll over $190,000 of your account to two outside IRAs. This would result in you having rolled $142,500 to a traditional IRA and $47,500 to a Roth IRA. You would have $10,000 left in your TSP account, consisting of $7,500 traditional and $2,500 Roth.
Then you roll the $142,500 from your traditional IRA back into the TSP. Now you will have $150,000 in your traditional TSP and $2,500 in your Roth TSP. If you took withdrawals from the TSP, the vast majority of the money you took would be from your traditional balance and only a small amount from the Roth balance.
The remainder of your Roth investments would be in an IRA and not subject to the requirement that you take required minimum distributions